Final answer:
The social media metric that best measures the number of followers who clicked and responded to a paid advertisement is engagement rate.
Step-by-step explanation:
The social media metric that best measures the number of followers who clicked and responded to a paid advertisement is engagement rate.
Engagement rate is calculated by dividing the total number of clicks and responses to the advertisement by the number of followers, and then multiplying by 100 to get a percentage. It measures the level of interaction and participation of followers with the paid advertisement, giving insight into its effectiveness.